The high light output per input power (lumens per watt) of discharge lamps makes it desirable to consider such lamps also for automotive head lamp use. One such type lamp uses a double-ended bulb, in elongated form, with current supply leads emanating from both and portions of the bulb. The lamp, additionally, includes a hollow base structure with terminal tabs, posts or blades, and a holder element for the lamp bulb itself. Additionally, the lamp includes a shielding element to obtain the unsymmetrical light distribution required by automotive standards.
Two-filament incandescent lamps used in automotive head lamps frequently include a shielding cap, located within the light bulb, in order to obtain the required light distribution from the two respective filaments, one for "high beam" and one for "low beam". Head lamps which are specifically designed to provide low-beam illumination only usually have a light shield located outside of the lamp bulb. Such a light shield may be associated with the reflector of the head light or with the socket of the lamp itself.